Drill-stem



I. LARI Aug. 25, 1970 DRILL-STEM 3 Sheets-Sheet 1 Filed June 18, 1968 Aug. 25, 1970 I. LARl 3,525,237

DRILL-STEM Filed June 18, 1968 3 Sheets-Sheet 2 I. LARI Aug. 25, 1970 DRILL-STEM 3 Sheets-Sheet 5 Filed June 18, 1968 United States Patent 3,525,237 DRILL-STEM Ioan Lari, Cimpina, Rumania, assignor to Ministerul Petrolului, Bucharest, Rumania Patented Aug. 25, 1970 a flow of drilling fluid in downward direction. At its ends,

Filed June 18 1968 Sen No. 738 048 5 The cross-section of the drill stem, as shown in FIG.

. 2, has the shape of a symmetrically curved equilateral I s CL 3 Claims triangle, the edges'f'c of which come in contact with the walls of the bore and are therefore preferably formed with a hard material for eliminating wear during opera- ABSTRACT OF THE DISCLOSURE 10 tion in the bore hole. Due to this shape of the drill stem, A drill stem is provided which comprises an elongated which can f f for example by rolling. h y havinga crosmection in the shah? of a carved ments of ax1all lnertla have equal values about all the equilateral triangle with equal axial of inertia i f g i g f 9 ifm f as WY axis which through 1 0f the 2. 6.1133? 23:5 823110.??? i'lami irifiiririfiirfi I base the mangle' about 80 to 90% larger than those of cylindrical drill stems.

At the same time, due to this shape, there is obtained, DRAWINGS apart from a good stability of the drill stem string, a larger FIG. 1 is a perspective view of a drill stem provided space for the upward circulation of the drilling fluid in accordance with one embodiment of the invention; simultaneously with the realization of a large weight per FIG. 2 is a cross-section through line AA of FIG. 1; unit length of drillstem.

FIG. 3 is an end view of the drill stem; The following table indicates in conjunction with FIGS. FIG. 4 shows a drill collar provided with thread boxes; 3, 4 and 5, various dimensions of operating arrangeand l ments: 5

. lBlt S Nominal size, 5 2: Thread E.D.in. mm. d d (I: l R r A.P.I.

, 142 43 103.0 111 s, 000 122. s 47.5 2% Reg 165 54 120.6 136.6 s, 000 142.8 52.0 3; Reg. 186 66 136.0 155.5 8,000 161.0 54.5 3% Fst. 213 79 155.4 184.0 3,000 184.4 57.3 4% Reg 241 91 116.4 212.5 8,000 203.7 62.0 515 Reg 298.5 108 182.6 269.5 s, 000 240.6 65.6 6% Reg DETAILED DESCRIPTION The invention relates to drill stems which permit a maximum load on the drilling bit and provide an automatic centering of the drill stem string in' a bore hole.

Drill stems" are known which have a round or square cross-section. The drill stems with a round section have the disadvantage that their weight per unit length is relatively low and centering devices are necessary to maintain the verticality of the bore. Drill stems with a square section have the disadvantage that free space for the upward circulation of drilling mud is too small and the development of technical operating accidents is possible.

A type of drill stem is also known which consists"%-of a central tube having around it three heavy cylindrical blocks which are solidly fixed by plates to the central tube. This type of drill stem has the disadvantage of having a complicated construction and the further disadvantage that, during operation in the bore hole, operating accidents might occur.

The drill stem according to the invention does away with these disadvantages due to the fact that, in order to realize a maximum weight per unit length and an assurance of a sufiicient large space for the downward flow of drilling fiuid and the stability of the string without the need for centering devices, the drill stein is provided with a cross-section having the shape of a curved equilateral triangle which has equal axial moments of inertia as to any axis passing through the center of the base circle of the cross-section of the curved equilateral triangle. This insures optimum stability of the drill stem string.

With reference to the drawings, the drill stem consists of a body 1 provided with a central channel a for passing FIG. 5 shows radius R for determining the sides of the curved equilateral triangle. Points 0 a and a of the equilateral triangle are the centers for drawing the circular arcs corresponding to the three sides of the curved triangle.

Any axis passing through center 0 (FIG. 5) is an inertia axis for the axial moments of inertia. The table indicates all the design details of several self-stabilizing drill collars. 1

FIG. 4 shows a drill collar fitted at both ends with coarse thread boxes of the tool-joint type. The drill collars are threadably connected through the medium of cylindrical stubs which are 500-800 mm. in length.

The drill stems characteristics according to the invention, have the following advantages:

They insure good stability of the drill stem string;

They realize the most weight per unit length, and

They insure a maximum space for upwards circulation of the fluid.

The central channel a flares outwardly at its ends.

What is claimed is:

1. A drill stem comprising an elongated body having a cross-section in the shape of a curved equilateral triangle with equal axial moments of inertia as to every axis which passes through the center of the base circle of the cross-section of the curved equilateral triangle, said body being provided with a central channel of circular cross-section for the downward flow of a drilling fluid therethrough, said body including tapered end portions, the channel having flared end portions in said tapered end portions of the body.

2. A drill stem as claimed in claim 1 wherein the body has three outermost portions at theapices of the triangle which are of a relatively hard material.

3. A drill stern as claimed in claim 2 wherein said curved triangle has side surfaces which extend along circular arcs struck from the opposite apex of the triangle.

References Cited UNITED STATES PATENTS 4 FOREIGN PATENTS 2/ 1958 Belgium. 2/ 1909 Germany.

5 JAMES A. WONG, Primary Examiner US. Cl. X.R. 

